1. Field of the Invention
The present invention relates to a reluctance-type motor which is multiple-phase half-wave energized.
2. Related Art
A reluctance-type motor produces high output torque and has simple construction. However, it is used in only limited fields, because it also produces high ripple in the output torque. When a protruded salient pole of a rotor and a protruded salient pole of a stator completely face each other, that is, align in phase, during the rotation of the rotor rotation, magnetic resistance between poles decreases thereby causing magnetic saturation and hence the ripple in the output torque.
The reluctance-type motor is typically constructed as shown in FIG. 8. A rotor has protruded poles 100 on a rotor ring 102, and a stator has protruded poles 101 on a stator ring 103. Poles 100 and 101 protrude from the rings 102 and 103, respectively. It is assumed that each protruded pole 100 of the rotor has the same widths rD1 and rD2 (rD1=rD2) at its bottom (root) and top (free end) in a rotation direction, and that each protruded pole 101 of the stator has the same widths sD1 and sD2 (sD1=sD2) at its bottom and top in a rotation direction. In this instance, the magnetic flux concentrates in the angled corner part between pole and the ring. As a result, the magnetic saturation occurs when poles 100 and 101 completely face each other in a radial direction, thus greatly decreasing the output torque as shown in FIG. 3A.
It is also assumed that the ring 102 has a width rW in the radial direction, which is less than a half of the width rD2 of pole 100 (rW less than 0.5xc3x97rD2), and that the ring 103 has a width sW in the radial direction, which is less than a half of the width sD2 of pole 101 (sW less than 0.5xc3x97sD2). In this instance, the magnetic flux generated in the pole cannot flow sufficiently into the ring thereby causing the magnetic maturation when poles 100 and 101 completely face each other. As a result, the output torque sharply decreases as shown in FIG. 4A resulting in the ripple in the output torque.
It is therefore an object of the present invention to provide a reluctance-type motor that has less drop in output torque and hence less ripple in the output torque even salient poles of a rotor and a stator completely face each other.
According to the present invention, a reluctance-type motor comprises a core for a rotor or a stator. The core has a cylindrical ring and a plurality of salient poles protruding from the ring in a radial direction of the ring. Each pole has a bottom width and a top width in a circumferential direction of the core at its bottom which is connected to the ring and at its top which is away from the ring, respectively. The bottom width (D1) is sized to be larger than the top width (D2), and the ring has a width in a radial direction of the core to allow at least a half of magnetic flux in the pole to pass through the ring.
Preferably, the width of the ring is sized to be larger than a half of the top width of the pole. The pole is shaped to have a round corner at the bottom or in a trapezoid in which the bottom width is larger than the top width. The core has a plurality of thin magnetic plates stacked in an axial direction of the core, each plate has a plurality slits in each protrusion which forms the pole, and each plate has a thickness which is less than 5 times of a maximum width of each slit.